Inkjet printers are used around the world to provide fast, high quality, and affordable printing in both small scale and large scale printing formats. Inkjet printheads typically comprise thermal inkjet (TIJ) or piezoelectric inkjet (PIJ) semiconductor devices that are digitally controlled to dispense small droplets of fluid quickly and accurately by creating pulses within ink-filled firing chambers. Within inkjet printing systems, sensing the levels and properties of ink in ink supply reservoirs is desirable for various reasons. Accurately sensing and reporting the correct level of ink in an ink cartridge, for example, enables printer users to prepare to replace finished ink cartridges, helps users to avoid wasting ink, and enables printing systems to trigger actions that help prevent low quality prints due to inadequate ink levels. Sensing different fluid properties can be useful, for example, to determine the health and age of ink, to differentiate between different types of ink, to determine whether the ink has been properly mixed, and so on.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.